1. Field of the Invention
The present invention generally relates to laser generating apparatus, and more particularly, is directed to an end pumped solid-state laser and pumping source thereof.
2. Description of the Prior Art
Conventionally, a laser light source is employed in order to efficiently pump or excite a solid-state laser.
More specifically, in a prior-art side pumping method where a laser light source pumps from a side face of a solid state laser rod such as Nd:YAG as shown in FIG. 1, a light resonator is composed of respective side faces of, for example, a cylindrical laser medium or laser rod 1. From the laser light source, a pumping or exciting light L1 is incident in the direction perpendicular to an axis O of the light resonator, that is, onto the side face of the laser rod 1.
The above-mentioned structure provides a wider area which is irradiated with the pumping light L1, whereby the whole light quantity of the pumping light L1 incident to the laser rod 1 can be correspondingly augmented, so that a laser light L0 having a large light intensity as a whole can be emitted from the laser rod 1. However, with the side pumping method is difficult to obtain a laser light L0 having a spot of short diameter.
For this reason, an end pumping method is employed for obtaining a laser light of a short spot diameter, where a pumping light L2 is incident to a laser rod 3 from the end face thereof to pump the same, as shown in FIG. 2. More specifically, mirrors 4, 5 are disposed in the vicinity of respective end faces of the laser rod 3, whereby a light resonator is formed as a whole for a laser light L0 emitted from the laser rod 3.
Further, the mirror 4 selectively transmits the pumping light L2, while the mirror 5 transmits a part of the laser light L0 and reflects the rest of the same, whereby the pumping light L2 is incident on one end face of the laser rod 3 through the mirror 4 to pump or excite the laser rod 3. The laser light L0 resonated by the light resonator composed of the mirrors 4, 5 is emitted through the mirror 5.
With the above structure, a region of the laser rod 3 on which the pumping light L2 is incident is pumped, whereby a laser light is induced and then emitted from this pumped region. It is therefore possible to generate a laser light L0 of a short spot diameter by reducing the beam diameter of the pumping light L2. Thus, a light beam emitted, for example, from a laser diode is incident to an end face of a laser rod as a pumping light to thereby generate a desired laser light LO from the laser rod.
For generating a laser light L0 with a short beam diameter and a large light quantity by pumping a laser rod with a pumping light by the end pumping method, it is necessary to pump the laser rod 3 with a pumping light L2 having a short beam diameter and a large light quantity, that is, a pumping light L2 having a large power density.
However, the laser diode can merely generate a light beam having approximately 1 W at present, and therefore it is a future problem how to enhance the intensity of the pumping light.
Though the end pumping method can generate the laser light L0 of a short spot diameter, it cannot efficiently pump a laser rod, thereby presenting a difficulty in enhancing the intensity of the laser light L0.
There has been proposed as one solution for this problem a method of generating a pumping light having a large light quantity by using an optical fiber bundle 7 as illustrated in FIG. 3 (OPTICS LETTERS/Vol. 13, No. 4/April 1988, pp 306-308, Fiber-bundle coupled, end pumped Nd:YAG laser).
More specifically, light beams emitted from laser diodes 8A-8N are led to respective optical fibers constituting the fiber optics bundle 7 to thereby guide and converge the light beams from the laser diodes 8A-8N by means of the fiber optics bundle 7. Then, a pumping light L3, which is appropriately converged for pumping a laser rod 12, is generated through lenses 9 and 10. The laser rod 12 is formed with a mirror surface on one end face thereof on the side of the fiber optics bundle 7 for selectively transmitting the pumping light L3, thereby forming an optical resonator by the end face having the mirror surface and a mirror 5.
Since the light beams emitted from the laser diodes 8A-8N are converged by the fiber optics bundle 7, the light quantity of the pumping light L3 is enhanced. Thus, if the light beams from a plurality of the high-output laser diodes are converged by the fiber optics bundle 7 to generate the pumping light L3, a laser light having a short spot diameter and a high light intensity can be emitted.
On the other hand, a high-output laser diode is configured to have a large stripe width which may be, for example, 100 .mu.m. For delivering a light beam outputted from such a laser diode to an optical fiber, it is necessary to employ an optical fiber having a diameter larger than the stripe width of the high-output laser diode, which is required by an optical coupling. As the result, the whole diameter of the fiber optics bundle 7 becomes large, which leads to increase in the beam diameter of the pumping light L3 outputted from the fiber optics bundle 7. Thus, the pumping light L3 having a large light intensity is provided, whereas the spot diameter of the pumping light L3 is larger, thereby presenting a difficulty in improving the power density.
Although a laser light having a large light intensity can be generated by applying the pumping light L3 to the end pumping method, the spot diameter of the laser light pumped by the pumping light L3 becomes larger corresponding to the spot diameter thereof.